1. Field of the Invention
The present invention relates to a distance measuring apparatus, and particularly to a distance measuring apparatus of, for example, a camera using a passive AF sensor.
2. Description of the Related Art
A distance measuring apparatus of a camera using a passive AF sensor forms images of a distance measurement object on a pair of left and right line sensors, for example, and obtains left and right sensor images (AF data). A pair of window ranges for obtaining a pair of AF data for use in correlation value calculation, of AF data obtained from the pair of left and right line sensors, are determined, and a pair of AF data for use in correlation value calculation are sequentially obtained, with the pair of window ranges being shifted in opposite directions in a pair of predetermined sensor areas (employed sensors). Alternatively, a pair of AF data for use in correlation value calculation are sequentially obtained, with one window range being fixed and the other window range being shifted. The correlation level of a pair of AF data obtained in this way is determined, and the distance from the distance measurement object is calculated according to the shift amount of the pair of window ranges providing the highest correlation level (in which left and right sensor images are consistent with each other).
If the signal amount level of the left AF data and the signal amount level of the right AF data are not consistent with each other, proper correlation cannot be obtained, and as a result erroneous distance measurement may occur. Japanese Patent Application Publication No. 8-285580 discloses that correlation value calculation is carried out after AF data is corrected so that the smallest value of the left AF data and the smallest value of the right AF data are consistent with each other. Japanese Patent Application Publication No. 5-264892 discloses that correlation value calculation is carried out after AF data is corrected so that the average value of the left AF data and the average value of the right AF data are consistent with each other.
However, in the conventional correction of AF data, AF data is corrected so that the smallest values or average values of AF data in the ranges of the employed sensor are consistent with each other, and therefore there may be cases where the signal amount levels of AF data are not consistent with each other if the ranges of distance measurement object imaged by a pair of employed sensors are not consistent with each other, resulting in erroneous distance measurement. Also, there are problems such that AF data is corrected regardless of the fact that the correction of AF data is not necessary, leading to the determination that distance measurement is impossible.